Phase errors in a mobile communication channel of wireless communication system are caused by signals through multi paths due to neighboring buildings or geographical circumstances. In particular, the phase errors in a mobile communication channel changes by movements of a mobile object. Consequently, a received signal should be recovered by estimating the phase errors for securing a reliable communication because the received signal transmitted from a transmitter is deteriorated by the phase errors.
On the other hand, in the wireless mobile communication system, channel codes are employed in a conventional coding technique in order to obtain a required coding performance with a minimized energy and bandwidth.
Particularly, a turbo code, which is one of the channel codes, shows an outstanding bit error correction performance in a repeated decoding process employing input and output values of soft decision. However, there is a problem that such a performance of turbo code may be expected only in the case that a receiver acquires a correct signal without phase errors.
Therefore, recently, there are many studies on the improved performance of turbo code by detecting and recovering the changes of the phase errors occurred in the multi path channel.
U.S. Pat. No. 6,442,219 discloses a method of carrier phase estimation using maximum likelihood (ML) that is a phase recovery method having low complexity. However, the above mentioned prior art may not provide the performance gain by characteristics of codes because it does not consider the structure of channel codes.
Further, U.S. Pat. No. 5,937,016 discloses a method of temporarily determining symbols by recombining output bits with a status of memory according to decoding depth given by viterbi decoding unit based on convolutional codes, and discloses a phase recovery algorithm implemented in a soft input soft output (SISO) decoding unit controlled by turbo codes. However, since above mentioned prior art use only temporarily determined symbols without considering a structure of channel codes may not provide a desired total gain of the decoding algorithm.
Korean patent No. 0362851 discloses a method that estimates fading size and noise spreading of a channel using soft decision output values of a turbo code decoder. The soft decision output values get feedback an input of a repeated channel estimation unit to thereby update tap values of the estimation unit.
Many recent mobile applications require error correcting codes with a very long codeword to provide high quality multimedia services, which make it difficult for phase error, remain constant over such a long codeword. In addition, even after the phase compensation, received samples with residual phase rotation would reduce instantaneous SNR and this again decrease the decoding performance.
In order to solve this problem, we propose a piece-wise carrier recovery algorithm with a multi-dimensional block turbo code consisted of independently decodable component codes. Here we mean the component code as the consisting one dimensional block code. We estimate the phase reference at each component code, instead of estimating at the whole product code. By this way, we can correct time varying phase within a period of a component code length.